looking for universal motor speed control using avr microcontroller

universal motor speed control using avr microcontroller

Controlling direction and speed of DC motor is very essential in many applications like

· Robotic application – to change direction and speed of moving robot

· Industrial application – to change direction and speed of rotating machinery

· Domestic application – to vary speed of battery (DC) operated portable fan

· Defence application – to rotate radar, automatic gun, tank gun in either direction

· Communication application – rotate dish antenna upward – downward or clockwise - anticlockwise

Thus we can count number of such applications where there is a need to change direction and/or speed of DC motor. The direction of DC motor can be controlled by just reversing the polarity of given supply. And for varying speed, there are various ways to vary speed of DC motor but the best amongst them is PWM – pulse width modulation technique. In this technique we shall vary the width of applied pulse that will vary average voltage applied to motor and its speed will change.

So this project demonstrates how to vary the speed and change the direction of simple 12V 500 RPM DC series motor using AVR microcontroller ATmega32.

The major building blocks of this system are as shown in figure that are ATmega32 and DC motor driver chip L293D. Along with them we need some push buttons for controlling and LEDs for indications. Each block is described briefly here.



Push buttons – five push buttons are given to run, stop, change speed and direction of DC motor

Button

Function

Button 1

Run motor in clockwise direction

Button 2

Run motor in anticlockwise direction

Button 3

Stop motor

Button 4

Increase speed

Button 5

Decrease speed


L293D chip – this chip takes input from micro controller and drives DC motor. The micro controller output current is not enough to drive DC motor directly. The chip has quad half H bridge drivers. It will provide up to 600 mA current to motor that is enough to drive it.



LED indications – six LEDs are used for different indications

LED

colour

indication

LED 1

red

Blinks when motor runs in clockwise direction

LED 2

green

Blinks when motor runs in anticlockwise direction

LED 3

Blue

Blinks when speed in increased

LED 4

Orange

Blinks when speed is decreased

LED 5

red

Lits ON when speed limit is maximum

LED 6

red

Lits ON when speed limit is minimum

AVR micro controller ATmega32 is low power, high performance, 8-bit, Advance RISC architecture based micro controller. It has 32 KB of in system programmable FLASH. Also it has built in peripherals like 10-bit, 8 channel ADC, 4 PWM channels, 1 16-bit and 2 8-bit timers/counters, USART, SPI, IIC etc. In this system it performs following tasks
· Scans push buttons continuously to get user input

· Give different indications on LEDs

· Run or stop DC motor

· Change direction or speed of motor

The circuit is made up of ATmega32, L293D and few discrete components like LEDs, registers, capacitors, push buttons etc

· 5 push buttons SW1 – SW5 are connected to PORTA pins PA0 to PA4. Also all port pins are pulled high through external pull up resistors as shown

· 4 LEDs LED1 – LED4 are connected to PORTD pins PD0 to PD3 through current limiting resistors

· PORTC pins PC0 and PC1 are connected to input of L293D chip. 2 LEDs LED5 and LED6 are also connected to these pins through current limiting resistors

· DC motor is connected to output of L293D chip

· A 16 MHZ crystal with two 22 pF capacitor is connected to crystal input pins XTAL1 & XTAL2

· Vcc supply of 5 V is connected to required pins of both chips and pull up resistors

· Additional 12 V supply is given to L293D chip for motor only